Gas sensors are used in many industrial, medical and commercial applications. For example, oxygen sensors are used in the monitoring of combustion engine environments to increase engine performance and reduce emission of green house gases. Ammonia sensors may be important for monitoring ambient ammonia concentrations related to many environmental issues such as acidification, human health and climate change through particle formation. Carbon dioxide sensors may also be widely used in food and medicine packages as a means of detecting spoilage. Additionally, gas sensors for chip-based applications may detect gas levels of effluents such as H2,(g), NOx,(g), CO(g), H2S(g),, chemical weapons, petrochemical products, alcohols, etc. for applications such as manufacture process monitoring, homeland security, health monitoring, and disease detection.